Preparation of composite substances



' June 4, 1935. A. s. RIGGS 2,003,609

PREPARATION OF COMPOSITE SUBSTANCES Filed Aug. 26, 1932 .mvaukrspn {Myer L975 A'ITORNEY 3.

Patented June 4,1935 I Alger S. Riggs, New York, N. Y assignor, by

mesne assignments, to Electrons, Inc. of Dela= ware, a corporation of Delaware Application August 26. 1932, Serial No. 630,559

14 Claims.

This invention relates to metallic compositions and process of making the same. Its object is to attain a strong, malleable andfcluctile composition of certain metals such as nickel or cobalt with other substances such as the oxides energy it.

of barium, strontium, calcium, or the like.

Such compositions find utility as material for cathodes in thermionic devices, although the invention is not limited to such use.

In its-broad aspect the process is applicable to the attainment of an intimate intermixture of substances, one or more of which may be metallic. It is especially useful when thedesired mixture cannot be obtained by melting the substances together.

In the accompanying drawing, Figs. 1 and 2 represent two types of apparatus adapted to be used in carrying out the process, and.

Figs. 3 and 4 illustrate two stages in the process of forming a billet from the mixture obtained from the apparatus shown in Fig. 1 or.

Fig. 2.

In Fig. l, which is partly sectional and partly diagrammatic, reference character. it represents a tube, a portion of which may be heated by the surrounding furnace ii, the heat being supplied by any suitable means, such as resistance elements it connected to a source of electrical Tube i0 is closed at one end by a removable member it and is provided at this end with a pipe l5 by which a reducing atmos phere, such as hydrogen, may be admitted to the tube. In the portion of the tube it] which is surrounded by furnace H, is placed a plug it having a face or target ll disposed at an angle to the longitudinal axis of the tube. The plug it is provided with a gas passage it and is positioned in the tube by means of a sleeve is therein. A container 20 is disposed a considerable distance above the tube and is provided with an outlet pipe iii. The how of a solution 22 from this container may be controlled by the valve 23 to form a series of drops 2t emerging from the end of pipe 2!. The ap paratus is arranged so that drops it fall through an opening 25 in the upper end of tube and strike the target ll. A water jacket 26 surrounds the lower portion .of the tube and is provided with inlet and outlet pipes 21 and 28, respectively.

It is preferable to-make the tube l0, plug It and sleeve l9 of a metal which is a constituent of the desired substance but if this is not convenient, the material for these parts should be such as will not interfere with the process.

In Fig. 2, which illustrates diagrammatically an alternative apparatus and method, a container 30 is provided with a plurality of pipes 3! and 32 for admitting solutions thereto and may have a bafiie 33 to aid in mixing thesolutions which may be heated before entering container 30, or the container itself may be provided with a source of heat as indicated at 34. The, pressure within the container is indicated by a gauge ll. tainer 30 we retort or oven 36, and terminates in a spray nozzle 31 capable of dividing the mixed solution into small drops as it enters the retort. An inlet pipe 38 admits gas to retort and an outlet pipe 30 permits the escape of this gas. Retort 36 may be heated by surrounding it with a casing and providing resistance elements therein as in Fig. l or it may be heated in any other suitable manner.

In Figs. 1 and 2, the pipes i5,.2l, 28, iii, 32, 35 and 38 are provided with control valves.

A pipe 35 leads from con- 3 Theprocess of forming the mixture which is ultimately worked into the desired composite substance will be described in connection with the making of a cathode material comprising a base metal, such as nickel or cobalt, having distributed therein an alkaline-earth oxide or a mixture of such oxides. For brevity, the descrip tion will be specific to barium oxide and nickel and the making of an electron-emissive cathode having the barium oxide uniformly distributed in the nickel in a state of miscibility approaching that of a solution.

Solutions of barium nitrate and nickel nitrate are prepared and mixedso that the relative amounts of nickel and barium in the combined solution will give the proportions-desired in the completed cathode material. The preferable solvent is water but other solvents may be used if they do not interfere with the desired chemical reactions of the dissolved substances or solute.

The portion of the tube 50 and its contents which are surrounded by the furnace l l are heated to a temperature of approximately 800 C. A'reducing atmosphere is provided in the tube, for instance, by a. current of hydrogen or other reducing gas entering by the pipe and flowing upward through the tube, the passage 18, and the opening 25, where it may be burned as indicated at 29. The solution of barium and nickel nitrates is placed in the container 20 and the valve 23 is adjusted to form a series of drops it which fall through the flame 20 and the opening 25. When the drops strike the surface H, which is also heated to about 800 C. the water or other solvent is explosively evaporated or flashed into vapor. The temperature is such that the nitrates are broken down to give metallic nickel and barium oxide; the oxides 'of nitrogen being removed by combination with the hydrogen and/or water vapor, the resulting products passing out through the opening 25. The evaporation of the solvent is so rapid that the precipitated nickel and barium oxide does not form large particles of either substance, and since each drop 24 contains nickel and barium in the same proportions as the main body of the solution 22, the resulting precipitate will contain nickel and barium in substantially the same proportions and in a state of intimate molecular mixture approaching that of the solution itself.

As the process continues the mixture of nickel and barium oxide collects on the target I! and various sized particles thereof drop into that portion of the passage l8 indicated at l8a. After a quantity of the mixture has been thus obtained the plug I6 is lowered to the portion of tube III which is surrounded by water Jacket 26 where it is cooled, and then the product, containing the molecularly mixed barium oxide and nickel, may be removed through the bottom of the tube.

The apparatus shown in Fig. 2 is better-suited to produce the product in larger quantities. Separate solutions of nickel nitrate and barium nitrate are forced underpressure and in the desired proportions into the container 30 through pipes 3| and 32. The solutions are preferably heated to a temperature of 100 to 150 C., either before entering the container 30 or by heating the container while the mixed solution is passing therethrough. The baffle 33 assures that the solutions are well mixed. The pressure in the container should be high enough to prevent boiling of theiolvent. The hot solution passes through pipe'SSand emerges from the spray nozzle 31 into the oven or retort, 36 which is filled with hydrogen admitted through pipe 38 and burned at the outlet 39. Retort 36 is maintained at a temperature of. approximatekv 800 C. The fine drops of solution emerging from the nozzle 31 are immediately vaporized at this temperature and broken down into metallic nickel and barium oxide, intimately mixed as previously described. The mixture collects in the bottom of the retort 36 as indicated at 50.

The mixture which is obtained from either apparatus is in various sized particles or lumps. These are ground to a powder and passed through a fine screen, say about 200' mesh. 'The barium oxide is so intimately mixed with the nickel as a result of the sudden precipitation from solution that each particle of this powder contains nickel and barium in substantially the same proportions as in the solution.

The fine powder is then formed into a billet by compressing the powder in a closed space or die. Fig. 3 illustrates such a die comprising a base plate 42, a hollow body 43 and a plunger 44. A

pressure of approximately 5 tons per square,

inch is exerted by the plunger to form the billet. For ribbon filaments the billet is preferably a disc, approximately th inch thick and half an inch in diameter. For wire filaments the billet is preferably a bar approximately 5th x th by 2 inches long. In the case of the bar it is again pressed in a direction at right angles to the first pressing, as shown in Fig. 4, by providing an enclosed space of less width by means of the hollow member 45 and a smallerplunger 46. A

- unsatisfactory results.

billet thus formed has sufficient mechanical strength to be handled and is heated at 800 C.

for approximately 15 minutes to further consolidate the particles.

The billet is then subjected to impact pressure by placing it in a closed die, similar to those of Figs. 3 and 4, and placing both the billet and die under a drop forge so that the hammer thereof is brought down upon the plunger, imparting a sudden blow thereto. The billet is then'annealed in a hydrogen atmosphere. The drop forging process may be repeated several times, until the desired ductility is obtained, the billet being annealed after each blow. Preferably the ductility is obtained with the least number of blows and therefore the highest obtainable impact pressure is desirable. In practice, impact pressures of the order of 1400 tons per square inch are obtained. The forged billet may be swaged, drawn or rolled into a wire or filament of desired cross section.

By the above described process it is possible to incorporate as much as 7% of barium, in the form of barium oxide, in a nickel core and satisfactory electron emissive filaments have been obtained containing from 3 to 7% of barium based on the total weight of the filament.

The above described process is not limited to the materials mentioned or to the production of electron eniissive filaments, but may be used to form intimate mixtures, without chemical combination, of metals or non-metals. For instance, magnesium may be thus intimately mixed with nickel, or magnesium oxide with iron.

-The foregoing description mentions only nitrates as the metallic salts for the solution from which the desired precipitate is obtained but other salts such as formates may be used with water or other solvents. A reducing atmosphere, in lieu of hydrogen, may be provided by the'chemical decomposition of such salts or the evaporation of the solvent.

I have found that the best results are obtained when the metal forming the active constituent is not readily absorbed by the base material. -For instance, a nickel base and barium oxide active material produce satisfactory thermionic emission but the combination of an iron base and barium oxide active material produces However, iron as a base with magnesium oxide produces satisfactory thermionic emission.

I have also found that it is preferable, though not essential, that instead of one alkaline-earth oxide two or more may be used, because a mixture of these .oxides provides an active material which is fusible, and therefore mobile, at the operating temperature of the cathode. A eutectic mixture of said oxides provides the lowest melting point. i

I claim:--

1. A metallic product having the ductility required for working into filamentary form and consisting of a base metal and an alkaline-- earth oxide in a state of molecular miscibility.

2. A metallic product having the ductility re-' quired for working into filamentary form and consisting of metallic nickel and barium oxide in a state of molecular miscibility.

3. A ductile product consisting of a mixture of metallic nickel and barium oxide in a state of molecular miscibility, in which the barium constitutes more than three per cent of the total weight of the aocaeoa 4. The process ot'mixing normally solid substances which do not readily melt together to form a homogeneous mixture comprising mixing solutions containing said substances as nonvolatile and mutually non-reactive constituents, dividing the mixed solution into small drops, and explosively evaporating the volatile portions thereof.

5. The process of combining a metal and a respectively and then precipitating the samev from the solution by flashing the solvent into vapor at a temperature well above its boiling point and at least equal to the decomposition temperature of said salts. 1

'7. The process which consists of dropping a solution containing nickel'nitrate and barium nitrate upon a hot bai'lie, subjecting the resultant product to high pressure, and then drop forging the same.

8. The process of making an electron emissive filament which comprises making solutions of compounds of metals at least one of which is capable of forming an electron emissive compound, mixing the solutions, dividing the resulting solution into drops and causing violent subdivision of said drops at a temperature to decompose said compounds with simultaneous evaporation of the volatile portions thereof, thereby precipitating the desired substances in solid form and intimately mixed, andworking the mixture into filamentary form. I

9. The process of incorporating an oxide oi. an alkaline-earth metal ina base metal which comprises explosively evaporating mixed solutions containing salts of the said metals.

10. A thermionic cathode material, comprising a nickel base and having intimately dispersed therein a eutectic mixture of barium and strontium oxides.

11. A thermionic cathode consisting of a base metal having intimately dispersed therein a eutectic mixture of the oxides of other metals which are electron emissive at moderate temperatures and do not readily alloy with said base metal.

12. The process of producing va composite substance having metalliferous components, which comprises dispersing in a reducing atmosphere a common solution containing a plurality of said components at a temperature sufficiently high to flash the solvent into vapor and deposit the said components in a. dry state, subjecting the resulting mixture to high pressure and then mechanically working the same.

13. The process of producing a composite substance having metalliferous components,

which comprises mixing solutions containing a said components in soluble form and dispersing the mixed solution at a temperature suiilciently high to vaporize the volatile portions thereof and to simultaneously deposit the said components in a dry state.

14. In a process of converting a billet containing an intimate mixture of metalliferous components into a ductile wire, the steps of subjecting the billet to impact pressure of the order of 1400 tons'per square inch, and anneal ing the billet in a reducing atmosphere.

ALGER- S. RIGGS. 

